Beat margarine and Zsweet together in a large bowl until light and fluffy, 2 to 3 minutes. Mix in flour, baking soda, and baking powder until it is the consistency of brown sugar. Beat in eggs. Fold in bananas and nuts until just combined.

Scrape the batter into the pan and spread evenly. Bake for 60 minutes. Let cool in the pan for 5 minutes and cool completely on a rack before serving.